Explanation:
The picture is lovely, but this
pretty
cosmic shell was
produced by almost unbelievable violence - created
when a star with nearly 20 times the mass
of the sun blasted away its outer layers in a spectacular
supernova explosion.
As the expanding debris cloud swept through surrounding interstellar
material, shock waves heated the gas causing the supernova remnant
to glow in x-rays.
In fact, it is possible that all supernova explosions create
similar shells,
some brighter than others.
Cataloged as G21.5-0.9, this
shell
supernova remnant is relatively faint,
requiring about 150 hours of x-ray data from the orbiting
Chandra
Observatory to create this false-color image.
G21.5-0.9 is about 20,000 light-years distant in the constellation
Scutum
and measures about 30 light-years across.
Based on the remnant's size, astronomers estimate that light
from the original stellar explosion
first
reached Earth several thousand years ago.